Fuel/air mixing system for fuel nozzle

ABSTRACT

A system includes a fuel nozzle. The fuel nozzle includes a central hub with a first annular passage extending along a longitudinal axis of the fuel nozzle. A flow conditioner is disposed along the first annular passage. The flow conditioner includes at least one of a straightening vane, a mesh screen, or a multi-passage body having multiple passages generally parallel with the longitudinal axis. An outer shroud is disposed about the central hub to define a second annular passage extending along the longitudinal axis of the fuel nozzle.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to fuel nozzles, and more specifically, to systems to increase fuel/air mixing within the fuel nozzles.

A gas turbine engine combusts a mixture of fuel and air to generate hot combustion gases, which rotate turbine blades to drive a load, such as an electrical generator. The gas turbine engine may include one or more fuel nozzles to direct the mixture of fuel and air into a combustion region of the gas turbine. In addition, the one or more fuel nozzles may be used to premix the fuel and the air. Unfortunately, poor mixing of the fuel and the air may reduce the flame stability within the combustion region. In addition, non-uniform mixtures of fuel and air may increase the amount of undesirable combustion byproducts, such as nitrogen oxides.

BRIEF DESCRIPTION OF THE INVENTION

Certain embodiments commensurate in scope with the originally claimed invention are summarized below. These embodiments are not intended to limit the scope of the claimed invention, but rather these embodiments are intended only to provide a brief summary of possible forms of the invention. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below.

In one embodiment, a system includes a fuel nozzle. The fuel nozzle includes a central hub with a first annular passage extending along a longitudinal axis of the fuel nozzle. A flow conditioner is disposed along the first annular passage. The flow conditioner includes at least one of a straightening vane, a mesh screen, or a multi-passage body having multiple passages generally parallel with the longitudinal axis. An outer shroud is disposed about the central hub to define a second annular passage extending along the longitudinal axis of the fuel nozzle.

In a second embodiment, a system includes a fuel nozzle. The fuel nozzle includes a first annular passage extending along a longitudinal axis of the fuel nozzle, a flow conditioner disposed along the first annular passage, and a plurality of premixing tubes disposed along the first annular passage downstream from the flow conditioner. Each tube of the plurality of premixing tubes includes an air inlet, a fuel inlet, and an air-fuel mixture outlet. The fuel nozzle also includes an outer shroud disposed about the central hub to define a second annular passage extending along the longitudinal axis of the fuel nozzle. In addition, the fuel nozzle includes a plurality of swirl vanes disposed in the second annular passage between the outer shroud and the central hub, wherein an interior of each swirl vane of the plurality of swirl vanes is configured to route a first air flow into the first annular passage, an exterior of each swirl vane of the plurality of swirl vanes is configured to swirl a second air flow along the second annular passage, and the flow conditioner in the first annular passage is disposed between the plurality of swirl vanes and the plurality of premixing tubes.

In a third embodiment, a system includes a fuel nozzle. The fuel nozzle includes a central hub having a first annular passage extending along a longitudinal axis of the fuel nozzle and a flow conditioner disposed along the first annular passage. The flow passage is at least one of a straightening vane, a mesh screen, or a multi-passage body having a plurality of passages generally parallel with the longitudinal axis. The fuel nozzle includes a plurality of swirl vanes disposed in the second annular passage between the outer shroud and the central hub, wherein an interior of each swirl vane of the plurality of swirl vanes is configured to route a first air flow into the first annular passage, an exterior of each swirl vane of the plurality of swirl vanes is configured to swirl a second air flow along the second annular passage, and the flow conditioner in the first annular passage is disposed between the plurality of swirl vanes and an outlet of the fuel nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic diagram of an embodiment of a gas turbine system having a combustor and fuel nozzles with features to improve fuel/air mixing;

FIG. 2 is a perspective view of an embodiment of the fuel nozzles of FIG. 1, illustrating the arrangement of the fuel nozzles within the combustor of the gas turbine system.

FIG. 3 is a perspective view of an embodiment of a fuel nozzle of FIG. 2 having various flow conditioners to improve fuel/air mixing;

FIG. 4 is a cross-sectional view of an embodiment of the fuel nozzle of FIG. 3 taken along line 4-4, illustrating a plurality of straightening vanes (e.g., coupled to an inner wall) to improve fuel/air mixing;

FIG. 5 is a simplified perspective view of an embodiment of a single straightening vane of FIG. 4 disposed between the inner wall and a hub wall of the fuel nozzle directly beneath an outlet of a vane curtain air passage, illustrating flow behavior in the absence and presence of the straightening vane;

FIG. 6 is a perspective view of an embodiment of the straightening vane 48 of FIGS. 4 and 5;

FIG. 7 is a cross-sectional view of an embodiment of the fuel nozzle of FIG. 3 taken along line 7-7, illustrating an annular segment with tubes or passages to improve fuel/air mixing;

FIG. 8 is a cross-sectional view of an embodiment of the annular segment of FIG. 7 taken along line 8-8, illustrating multiple passages through the annular segment; and

FIG. 9 is a cross-sectional view of an embodiment of the fuel nozzle of FIG. 3 taken along line 4-4, illustrating a plurality of straightening vanes (e.g., coupled to the hub wall) to improve fuel/air mixing.

DETAILED DESCRIPTION OF THE INVENTION

One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

The present disclosure is directed toward systems for improving fuel and air mixing within fuel nozzles of combustors. In particular, air is directed through a swirler and into one or more premixing tubes (e.g., a group of 10 to 100 premixing tubes). A flow conditioner is disposed between the swirler and the premixing tubes, such that the flow conditioner generally straightens (e.g., axially) the flow of air into the premixing tubes. Straightening the flow of air results a more uniform delivery of air into the premixing tubes, thereby improving fuel/air mixing and increasing the efficiency of the combustor.

In certain embodiments, the flow conditioner may be one or more straightening vanes or an annular segment with a plurality of passages or tubes disposed therethrough. As will be discussed further below, the straightening vane is shaped like an airfoil and is partially or entirely arcuate in an axial and circumferential direction of the fuel nozzle. The arcuate shape reduces the circumferential velocity (e.g., swirl) of the air, thereby straightening (e.g., axially) the air upstream of the premixing tubes. In another embodiment, the flow conditioner may be the annular segment having the plurality of passages or tubes. The passages or tubes are generally straight and serve to straighten the air and to direct the air towards the premixing tubes with a decreased swirl. Again, the decreased swirl axially straightens the air, which improves fuel/air mixing within the fuel nozzle and increases the efficiency of the combustor, and subsequently, the gas turbine system.

As used herein, the term “annular” shall mean a ring-shaped. The use of the term “annular” is not intended to limit the scope of the present disclosure with respect to the shape, perimeter, or other geometric feature of the hollow structure. That is, a hollow cylinder, a hollow cone, a hollow polyhedron, a hollow prism, and the like, are all encompassed by the term “annular”.

Turning now to the figures, FIG. 1 illustrates a block diagram of an embodiment of a gas turbine system 10 with a fuel nozzle 12 (e.g., turbine fuel nozzle) designed to increase mixing of fuel and air. Throughout the discussion, a set of axes will be referenced. These axes are based on a cylindrical coordinate system and point in an axial direction 14, a radial direction 16, and a circumferential direction 18. For example, the axial direction 14 extends along a longitudinal axis 17 (shown in FIG. 3) of the fuel nozzle 12, the radial direction 16 extends away from the longitudinal axis 17, and the circumferential direction 18 extends around the longitudinal axis 17.

As illustrated, the gas turbine system 10 includes a compressor 20, a combustor 22 (e.g., turbine combustor), and a turbine 24. The turbine system 10 may include one or more of the fuel nozzles 12 described below in one or more combustors 22. The compressor 20 receives air 26 from an intake 28 and compresses the air 26 for delivery to the combustor 22. As shown, a portion of the air 26 is routed to the fuel nozzle 12, where the air 26 may premix with fuel 30 before entering the combustor 22. The air 26 and the fuel 30 are fed to the combustor 22 in a specified ratio suitable for combustion, emissions, fuel consumption, power output, and the like. Unfortunately, if the air 26 and the fuel 30 are not well mixed, the flame stability within the combustor 22 may be reduced. Accordingly, the fuel nozzle 12 includes a flow conditioner within an annular passage of the fuel nozzle 12. The flow conditioner straightens the air 26 (e.g., in the axial direction 14) and improves the mixing of the air 26 and the fuel 30 by providing a uniform distribution of air downstream to the premixing tubes, as will be discussed further below.

The mixture of the air 26 and the fuel 30 is subsequently combusted in the combustor 22, forming hot combustion products. The hot combustion products enter the turbine 24 and force blades 32 of the turbine 24 to rotate, thereby driving a shaft 34 of the gas turbine system 10 into rotation. The rotating shaft 34 provides the energy for the compressor 20 to compress the air 26. For example, in certain embodiments, compressor blades are included as components of the compressor 20. Blades within the compressor 20 may be coupled to the shaft 34, and will rotate as the shaft 34 is driven to rotate by the turbine. In addition, the rotating shaft 34 may rotate a load 36, such as an electrical generator or any device capable of utilizing the mechanical energy of the shaft 34. After the turbine 24 extracts useful work from the combustion products, the combustion products are discharged to an exhaust 38.

As noted previously, the gas turbine system 10 includes one or more fuel nozzles 12 with features to improve uniformity in the air distribution and the mixing of the air 26 and the fuel 30. FIG. 2 illustrates an arrangement of the fuel nozzles 12 within the combustor 22 of the gas turbine system 10. As shown, six fuel nozzles 12 are mounted to a head end 40 of the combustor 22. However, the number of fuel nozzles 12 may vary. For example, the gas turbine system 10 may include 1, 2, 3, 4, 5, 10, 50, 100, or any other number of fuel nozzles 12. The six fuel nozzles 12 are disposed in a concentric arrangement. That is, five fuel nozzles 12 (e.g., outer fuel nozzles 42) are disposed about a central fuel nozzle 44. As will be appreciated, the arrangement of the fuel nozzles 12 on the head end 40 may vary. For example, the fuel nozzles 12 may be disposed in a circular arrangement, in a linear arrangement, or in any other suitable arrangement. The flow of the air 26 and the fuel 30 within the fuel nozzles 12 is discussed below with respect to FIG. 3.

FIG. 3 is a perspective view of an embodiment of the fuel nozzle 12 equipped with flow conditioners 46 (e.g., straightening vanes 48, mesh screen 50, and annular multi-passage segment 52) to straighten and uniformly distribute a flow of the air 26 and improve the mixing of the fuel 30 and the air 26. In other words, the flow conditioners 46 may reduce large scale vortices, small scale eddies, and other swirling motion, while also helping to distribute the air more uniformly across the air flow passage (e.g., more uniform velocity across the entire cross section). Although the straightening vanes 48, mesh screen 50, and annular segment 52 are illustrated in use within a singular fuel nozzle 12, it should be noted that the various flow conditioners 46 may be used independently or in other combinations. For example, an embodiment of the fuel nozzle 12 may include the straightening vanes 48 but not the mesh screen 50 or the annular segment 52. Alternatively, the fuel nozzle 12 may include the mesh screen 50 and/or the annular segment 52 but not the straightening vanes 48. Thus, it will be appreciated that the selection of the flow conditioners 46 may be based on various factors, such as pressure drop, flow rates, and the like.

The various flow conditioners 46, used independently or in combination with each other, may provide varying degrees of air straightening in the axial direction 14 (i.e., may reduce the swirl of the air 26 by varying amounts or percentages). In certain embodiments, it may be desirable to provide the fuel nozzles 12 with varying amounts of swirl, depending on their placement about the head end 40 of the combustor 22. For example, it may be desirable to straighten air flow within the central fuel nozzle 44 (e.g., upstream of the premixing tubes 70) in order to improve flame stability. Accordingly, the outer fuel nozzles 42 and the central fuel nozzle 44 may be equipped with different flow conditioners 46. That is, in certain embodiments, the central fuel nozzle 44 may include the straightening vanes 48, whereas the outer fuel nozzles 42 include both the mesh screen 50 and the annular segment 52. In yet other embodiments, the central fuel nozzle 44 may include one of the flow conditioners 46, while the outer fuel nozzles lack the flow conditioners 46. Again, the fuel nozzles 12 may employ any combination of the straightening vanes 48, the mesh screen 50, and the annular segment 52 to reduce the swirl of the air 26. It should be noted that when more than one flow conditioner 46 is employed, their ordering may be implementation-specific. For example, although the mesh screen 50 is illustrated as upstream of the annular segment 52, in other embodiments, the mesh screen 50 may be downstream of the annular segment 52. As shown, the mesh screen 50 (e.g., perforated sheet) is a permeable grid of material (e.g., plastic, metal, ceramic, etc.) with small openings 51 that allow fluid to pass through. The openings 51 may vary in size, and may be, for example, between approximately 5 to 50 mm, or 0.1 to 20 mm, and all subranges therebetween. The mesh screen 50 extends crosswise (e.g., circumferentially 18) to the longitudinal axis 17 of a first annular passage 60 defined below. The mesh screen 50 may further axially straighten the air 26 and/or help distribute the air 26 more uniformly across the flow passage.

The geometry of the fuel nozzle 12 is discussed below. As illustrated, the fuel nozzle 12 includes a central hub 53 with an inner wall 54 and a hub wall 56 (e.g., outer wall of the central hub 53). The inner wall 54 defines a central passage 58 (e.g., inner cylindrical passage), and the hub wall 56 defines the first annular passage 60 that surrounds the central passage 58. During operation of the fuel nozzle 12, liquid fuel may be routed through the central passage 58 in the axial direction 14, as shown by arrows 62. The central hub 53 increases the flexibility of the fuel nozzle 12 by enabling liquid fuels to be used in combination with gas fuels for combustion within the combustor 22.

An outer wall 64 surrounds the hub wall 56, defining a second annular passage 66. The second annular passage 66 surrounds both the first annular passage 60 and the central passage 58. During operation of the fuel nozzle 12, the fuel 30 is routed through the second annular passage 66 in the axial direction 14, as shown by arrows 68. The fuel 30 enters premixing tubes 70 in the radial direction 16 through fuel holes or inlets 71 located in a side wall 73 of the premixing tube 70, as indicated by arrows 72. The premixing tubes 70 are circumferentially 18 distributed about the annular passage 60. Air 26, via the first annular passage 60, enters air inlets 75 of the premixing tubes 70 and flows in the axial direction 14 towards outlets 76 (e.g., air-fuel mixture outlets) of the premixing tubes 70. Within the premixing tubes 70, the fuel 30 mixes with the air 26 to form a combustible mixture and is directed into the combustor 22 via the outlets 76.

A shroud 78 (e.g., annular shroud wall) is disposed about the outer wall 64, defining a third annular passage 80. The third annular passage 80 surrounds the second annular passage 66, the first annular passage 60, and the central passage 58. As depicted, the third annular passage 80, the second annular passage 66, the first annular passage 60, and the central passage 58 are concentrically arranged with respect to the longitudinal axis 17 of the fuel nozzle 12. A first portion of the air 26 enters the third annular passage 80 upstream of a swirler 84 and travels in the axial direction 14 toward the outlet 74 of the fuel nozzle 12, as indicated by arrows 82. However, a second portion of the air 26 (e.g., vane curtain air) enters the first annular passage 60 radially 16 through the swirler 84, which includes one or more swirl vanes 86 circumferentially 18 spaced about an axis 17 of the fuel nozzle 12. More specifically, the second portion of the air 26 may enter the first annular passage 60 through the vane curtain air passages 83 disposed within the swirl vanes 86. The fuel 30 may enter the second annular passage 66 and flow through fuel passages 81 disposed within the swirl vanes 86 (upstream of the vane curtain air passages 83) and subsequently injected through fuel holes 79 into the third annular passage 80, where the fuel 30 may mix with the air 26 and enter the combustor.

Once the vane curtain air enters the first annular passage 60, the air 26 passes through one or more flow conditioners 46, as shown by arrows 85. The flow conditioners 46 straighten the flow of the air 26 (e.g., in the axial direction 14) upstream of the premixing tubes 70, which provides a uniform distribution of the air 26 to the premixing tubes 70 and improves fuel/air mixing within the premixing tubes 70 and the overall efficiency of the gas turbine system 10.

As shown, the flow path of the vane curtain air is defined by a flow length or axial distance 87 from the vane curtain air passages 83 of the swirler 84 to an upstream end 89 of the premixing tubes 70. The flow conditioners 46 are disposed along the flow length 87 (between the swirler 84 and the premixing tubes 70) to straighten and uniformly distribute the vane curtain air before it enters the premixing tubes 70. In certain embodiments, the flow conditioners 46 may be disposed within the first air passage 60 directly at the outlet of the swirler 84 or at the inlet of the premixing tubes 70 (see FIG. 5). As depicted, the straightening vanes 48 are located downstream of where the air 26 exits from the vane curtain air passages 83 of the swirler 84 (e.g., swirl vanes 86) into the first air passage 60 and upstream of the other flow conditioners 46 (e.g., mesh screen 50 and annular segment 52) and the premixing tubes 70. As will be appreciated, the amount of straightening provided by the flow conditioners 46 may be affected by the length of the flow conditioners 46, as is discussed in greater detail with respect to FIGS. 6 and 8.

Returning to FIG. 3, as the air 26 enters the first annular passage 60, the swirler 84 imparts a circumferential velocity to the air 26. The air 26 flows axially 14 and circumferentially 18 towards the flow conditioners 46, which axially 14 straighten the flow of the air 26 by reducing its circumferential velocity. Again, an axially straightened flow of air provides a uniform distribution of air 26 to the premixing tubes 70, thus improving the mixing of the fuel 30 and the air 26 within the premixing tubes 70 and the efficiency of the gas turbine system 10. In particular, the straightened flow may result in a more uniform equivalence ratio (i.e., ratio of the actual fuel/air ratio to the stoichiometric fuel/air ratio) between each of the premixing tubes 70 and in each premixing tube 70. For example, the equivalence ratios within each premixing tube 70 may be between approximately 0.3 to 0.7, 0.4 to 0.6, or 0.53 to 0.56, and all subranges therebetween. The increased uniformity of equivalence ratios (e.g., less than 1, 5, or 10 percent variance) among the premixing tubes 70 improves the flame stability within the combustor 22. Features of the flow conditioners 46 to straighten the air 26 to improve the uniformity of the equivalence ratios are discussed in further detail below with respect to FIGS. 4-8.

FIG. 4 is a cross-sectional view of the fuel nozzle 12 of FIG. 3, taken along line 4-4. As shown, a plurality of straightening vanes 48 is disposed within the first annular passage 60. For example, the fuel nozzle 12 may generally include approximately 1, 2, 3, 4, 5, 6, or any other number of straightening vanes 48. The straightening vanes 48 may be coupled to the inner wall 54 and extend from the inner wall 54 towards the hub wall 56 as depicted in FIG. 4. Alternatively, the straightening vanes 48 may be coupled to the hub wall 56 and extend from the hub wall 56 towards the inner wall 54 as depicted in FIG. 9. The straightening vanes 48 are arcuate in the circumferential direction 18 and the axial direction 14 (see FIG. 5), which enables a greater contact area between the flowing air 26 and the straightening vane 48. In addition, the straightening vanes 48 are circumferentially 18 spaced about the first annular passage 60, which improves the uniformity of the air 26 as it flows along the straightening vanes 48.

As illustrated, vane curtain air (e.g., air 26) flows radially 16 through the vane curtain air passages 83 of the swirl vanes 86 of the swirler 84, as shown by arrows 88. The air 26 exits the swirler 84 into the first annular passage 60 of the central hub 53. The radial entrance of the air 26 into the first annular passage 60 results in a circumferential velocity about the axis 17 of the fuel nozzle 12, which may decrease the uniform profile of the air across the first annular passage 60 and the premixing tubes 70. The air 26 continues to flow axially 14 and circumferentially 18 about the annular passage 60 until it encounters the straightening vanes 48. When the air 26 encounters the straightening vanes 48, they guide the air 26 along the axial direction 14, thereby reducing the circumferential velocity of the air 26. Accordingly, the shape of the straightening vanes 48 is designed to reduce the circumferential velocity of the air 26, as illustrated by FIG. 5.

FIG. 5 is a simplified perspective view of an embodiment of a single straightening vane 48 of FIG. 4 disposed within the inner wall 54 and the hub wall 56 of the fuel nozzle 12 directly beneath an outlet 90 of the vane curtain air passage 83, illustrating flow behavior in the absence and presence of the straightening vane 48. Portions of the fuel nozzle 12 are not illustrated to facilitate explanation of the flow behavior. As described above, the straightening vane 48 is disposed within the first annular passage 60. The straightening vane 48 may be coupled to the inner wall 54 and extend from the inner wall 54 towards the hub wall 56 within the first annular passage 60. Alternatively, the straightening vane 48 may be coupled to the hub wall 56 and extend from the hub wall 56 towards the inner wall 54 with the first annular passage 60. The straightening vane 48 is arcuate in the circumferential direction 18 (see FIG. 4) and the axial direction 14, which enables a greater contact area between the flowing air 26 and the straightening vane 48. The straightening vane 48 includes an upstream end portion 92 (e.g., leading edge) and a downstream end portion 94 (e.g., trailing edge) relative to the general direction of the flow of the air 26 in the axial direction 14. The upstream end portion 92 includes a non-linear or arcuate portion 96 and the downstream end portion 94 includes a linear or straight portion 98. The straightening vane 48 gradually turns from the radial direction 16 toward the axial direction 14 along the longitudinal axis 17 of the fuel nozzle 12 in the downstream direction (i.e., axial direction 14) toward the outlet 74 of the fuel nozzle 12.

As depicted in FIG. 5, the air 26 flows radially 16 thorough the vane curtain air passage 83 into the first annular passage 60, the air 26 enters off-center relative to the axis 17 (see FIG. 4). In the absence of the straightening vane 48, the off-centered entrance of the air 26 creates a swirling flow 100 (represented by the double dotted-dashed line) that flows in both the circumferential 18 and axial 14 directions. The circumferential velocity of the swirling flow 100 about the axis 17 of the fuel nozzle 12 may decrease the uniform profile of the air 26 across the first annular passage 60 and the premixing tubes 70, while also resulting in a pressure drop within the first annular passage 60.

The presence of the straightening vane 48 straightens the flow of the air 26 within the first annular passage 60 (as indicated by dashed line 102), while reducing the amount of pressure drop (e.g., relative to the pressure drop in the absence of the straightening vane 48) within the first annular passage 60. As the air 26 exits the outlet 90 of the vane curtain air passage 83, it encounters the arcuate portion 96 of the upstream end portion 92 of the straightening vane 48. The arcuate portion 96 gradually or smoothly transitions from the upstream end portion 92 to the downstream portion 94 of the straightening vane 48. This gradual transition may reduce the amount of pressure drop experienced by the air 26 as it enters and flows along the first annular passage 60. Upon encountering the upstream end portion 92 of the straightening vane 48, the air 26 (i.e., dashed line 102) flows downstream along the arcuate portion 96 to the straight portion 98 of the downstream end 94 of the straightening vane 48. The flow of the air 26 (i.e., dashed line 102) results in the gradual straightening of the air flow 26 to flow generally in the axial direction 14.

FIG. 6 is a perspective view of the straightening vane 48 of FIGS. 4 and 5. In general, the straightening vane 48 is as described above. As shown, the arcuate portion 96 gradually decreases in curvature (e.g., angle with respect to the axial direction 14 relative to the straight portion 98 of the straightening vane) from the upstream end portion 92 to the downstream end portion 94 until the straightening vane 48 transitions into the straight portion 98. The gradual decrease enables a gradual reduction in the circumferential velocity of the air 26. In certain embodiments, the arcuate portion 96 may be a partial paraboloid, hyperboloid, or another quadric surface, or any other suitable curved shape that gradually decreases in curvature. For example, angle 104 near a proximal or upstream end of the arcuate portion 96 may be between approximately 20 to 100, 40 to 60, or 45 to 50 degrees, and all subranges therebetween. In certain embodiments, angle 106 near a distal or downstream end of the arcuate portion 96 (and downstream of angle 104) may be between approximately 0 to 30, 5 to 20, or 10 to 15 degrees, and all subranges therebetween. The angle 106 is less than the angle 104, which provides a smooth and gradual reduction in the circumferential velocity of the air 26.

The straightening vane 48 has an axial length 108 from the upstream end portion 92 to the downstream end portion 94. As noted earlier, the axial length 108 may affect the straightening of the air 26. In general, a longer axial length 108 increases the straightening of the air 26. Thus, in certain embodiments, the axial length 108 may be between approximately 5 to 95, 20 to 80, or 40 to 60 percent, and all subranges therebetween, of the total axial distance 87 along the first annular passage 60 from the vane curtain air passages 83 of the swirler 84 to the upstream end 89 of the premixing tubes 70 (see FIG. 3), in order to reduce the swirl of the air 26 and improve the efficiency of the gas turbine system 10. The arcuate portion 96 has an axial length 107 and the straight portion 98 has an axial length portion 109. In some embodiments, the axial length 107 of the arcuate portion 96 may be longer than the axial length 109 of the straight portion 98. In other embodiments, the axial length 109 of the straight portion 98 may be longer than the axial length 107 of the arcuate portion 96. In certain embodiments, the axial length 107 of the arcuate portion 96 may be approximately 5 to 95, 15 to 65, or 30 to 50 percent, and all subranges therebetween, of the axial length 108 of the straightening vane 48. In certain embodiments, the axial length 109 of the straight portion 98 may be approximately 5 to 95, 15 to 65, or 30 to 50 percent, and all subranges therebetween, of the axial length 108 of the straightening vane 48.

FIG. 7 is a cross-sectional view of the fuel nozzle 12 of FIG. 3, taken along line 7-7. As shown, the multi-passage body or annular segment 52 is disposed within the first annular passage 60 of the central hub 53. The annular segment 52 encloses a portion of the volume between the inner wall 54 and the hub wall 56. The annular segment 52 includes a solid body 110 that includes a plurality of passages or tubes 112 (e.g., cylindrical tubes) that extend throughout the solid body 110 in the axial direction 14 through which the air 26 can flow. The passages or tubes 112 are generally parallel with the longitudinal axis 17. The annular segment 52 may include any number of the passages or tubes 112, such as 1, 2, 3, 4, 5, 10, 20, or any other number. The tubes or passages 112 may include any cross-sectional shape (e.g., elliptical, rectilinear, etc.). The cross-sectional area of each passage or tube 112 may be uniform or vary between passages or tubes 112. The tubes or passages 112 may be arranged in a symmetrical (or uniform) pattern. For example, as depicted, the passages or tubes 112 are arranged concentrically in rows 114 about the axis 17. In other embodiments, the tubes or passages 112 may be arranged in non-symmetrical (or non-uniform) pattern. The arrangement of passages or tubes 112 of the annular segment 52 functions to axially straighten the flow of the air 26 as it passes through the annular segment 52 from an upstream axial end 116 to a downstream axial end 118 (see FIG. 8). In particular, the annular segment 52 straightens the air 26 that entered the first annular passage 60 via the vane curtain air passages 83 prior to reaching the premixing tubes 70 to provide a uniform profile of air 26 in each premixing tube 70, which reduces the variation in the amount of air 26 in each premixing tube 70.

FIG. 8 is a cross-sectional view of the annular segment 52 of FIG. 7, taken along line 8-8. As shown, the vane curtain air 26 flows from the upstream axial end 116 to the downstream axial end 118 of the annular segment 52, as shown by arrows 120. The air 26 follows the general shape of the passages or tubes 112, which are generally parallel with the axis 17 in the axial direction 14. Thus, the air 26 generally axially straightens as it flows from the upstream axial end 116 to the downstream axial end 118.

As shown, the annular segment 52 extends an axial length 122. In general, a longer axial length 122 provides longer passages or tubes 112, which increases the straightening of the air 26, but also increases pressure drop through the annular segment 52. Accordingly, in certain embodiments, the axial length 122 may be optimized by having a length between approximately 5 to 95, 20 to 80, or 40 to 60 percent, and all subranges therebetween, of the total axial distance 87 along the first annular passage 60 from the vane curtain air passages 83 of the swirler 84 to the upstream end 89 of the premixing tubes 70 (see FIG. 3). As noted earlier, the annular segment 52 may be employed with the mesh screen 50, which may be either upstream or downstream of the annular segment 52. Also, in certain embodiments, the mesh screen 50 may only be used.

FIG. 9 is a cross-sectional view of an embodiment of the fuel nozzle 12 of FIG. 3 taken along line 4-4, illustrating the plurality of straightening vanes 48. The fuel nozzle 12 and straightening vanes 48 are as generally described above. As depicted, the straightening vanes 48 are coupled to the hub wall 56 and extend from the hub wall 56 towards the inner wall 54.

Technical effects of the disclosed embodiments include providing the flow conditioners 46 to axially straighten the flow of the air 26 within the first annular passage 60 of the fuel nozzle 12. Straightening the air 26 uniformly distributes the air 26 into the premixing tubes 70, thus improving the mixing of fuel and air within the premixing tubes 70 of the fuel nozzle 12, thereby increasing the efficiency of the gas turbine system 10. The flow conditioner 46 may be the straightening vanes 48, the mesh screen 50, the annular segment 52, or any combination thereof.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

1. A system, comprising: a fuel nozzle, comprising: a central hub comprising a first annular passage extending along a longitudinal axis of the fuel nozzle and a flow conditioner disposed along the first annular passage, wherein the flow conditioner comprises at least one of a straightening vane, a mesh screen, or a multi-passage body having a plurality of passages generally parallel with the longitudinal axis; and an outer shroud disposed about the central hub to define a second annular passage extending along the longitudinal axis of the fuel nozzle.
 2. The system of claim 1, comprising a combustor or a gas turbine engine having the fuel nozzle.
 3. The system of claim 1, comprising a plurality of premixing tubes downstream from the flow conditioner, wherein each tube of the plurality of premixing tubes comprises an air inlet, a fuel inlet disposed in a side wall, and an air-fuel mixture outlet.
 4. The system of claim 1, comprising a plurality of swirl vanes disposed in the second annular passage between the outer shroud and the central hub, wherein an interior of each swirl vane of the plurality of swirl vanes is configured to route a first air flow into the first annular passage, an exterior of each swirl vane of the plurality of swirl vanes is configured to swirl a second air flow along the second annular passage, and the flow conditioner in the first annular passage is disposed between the plurality of swirl vanes and an outlet of the fuel nozzle.
 5. The system of claim 1, wherein the flow conditioner comprises a plurality of straightening vanes each gradually turning from a radial direction toward an axial direction along the longitudinal axis in a downstream direction toward an outlet of the fuel nozzle.
 6. The system of claim 1, wherein the central hub comprises a first wall extending circumferentially about the longitudinal axis to define a central passage, a second wall extending circumferentially about the first wall to define the first annular passage, and a third wall extending circumferentially about the second wall to define a third annular passage, wherein the first annular passage routes a first air flow along the flow conditioner, and the third annular passage routes a first fuel flow.
 7. The system of claim 6, wherein the second annular passage comprises a swirler and the first annular passage comprises a plurality of premixing tubes disposed downstream from the flow conditioner, wherein each tube of the plurality of premixing tubes comprises an air inlet, a fuel inlet in a side wall, and an air-fuel mixture outlet.
 8. The system of claim 7, wherein the straightening vane, the perforated sheet or mesh screen, and the multi-passage body are configured to reduce swirl in the first annular passage caused by the swirler in the second annular passage.
 9. A system, comprising: a fuel nozzle, comprising: a central hub comprising a first annular passage extending along a longitudinal axis of the fuel nozzle, a flow conditioner disposed along the first annular passage, and a plurality of premixing tubes disposed along the first annular passage downstream from the flow conditioner, wherein each tube of the plurality of premixing tubes comprises an air inlet, a fuel inlet, and an air-fuel mixture outlet; an outer shroud disposed about the central hub to define a second annular passage extending along the longitudinal axis of the fuel nozzle; and a plurality of swirl vanes disposed in the second annular passage between the outer shroud and the central hub, wherein an air passage of each swirl vane of the plurality of swirl vanes is configured to route a first air flow into the first annular passage, an exterior of each swirl vane of the plurality of swirl vanes is configured to swirl a second air flow along the second annular passage, and the flow conditioner in the first annular passage is disposed between the plurality of swirl vanes and the plurality of premixing tubes.
 10. The system of claim 9, comprising a gas turbine engine, wherein the gas turbine engine comprises the fuel nozzle, a combustor having the fuel nozzle, a compressor, and a turbine.
 11. The system of claim 9, wherein the flow conditioner comprises a straightening vane, a perforated sheet or mesh screen, or a multi-passage body having a plurality of passages generally parallel with the longitudinal axis.
 12. The system of claim 9, wherein the flow conditioner comprises a plurality of straightening vanes each having a turn gradually directed along the longitudinal axis in a downstream direction toward the plurality of premixing tubes.
 13. The system of claim 9, wherein the flow conditioner comprises a perforated sheet or mesh screen extending crosswise to the longitudinal axis in the first annular passage.
 14. The system of claim 9, wherein the flow conditioner comprises a multi-passage body having a plurality of passages generally parallel with the longitudinal axis.
 15. The system of claim 9, wherein the flow conditioner comprises a perforated sheet or mesh screen disposed with the first annular passage upstream of a multi-passage body having a plurality of passages generally parallel with the longitudinal axis.
 16. The system of claim 9, wherein the central hub comprises a first wall extending circumferentially about the longitudinal axis to define a central passage, a second wall extending circumferentially about the first wall to define the first annular passage, and a third wall extending circumferentially about the second wall to define a third annular passage, wherein the first annular passage routes the first air flow to the air inlet of each tube of the plurality of premixing tubes, and the third annular passage routes a fuel flow to the fuel inlet of each tube of the plurality of premixing tubes.
 17. A system, comprising: a fuel nozzle, comprising: a central hub comprising a first annular passage extending along a longitudinal axis of the fuel nozzle and a flow conditioner disposed along the first annular passage, wherein the flow conditioner comprises at least one of a straightening vane, a perforated sheet or mesh screen, or a multi-passage body having a plurality of passages generally parallel with the longitudinal axis; an outer shroud disposed about the central hub to define a second annular passage extending along the longitudinal axis of the fuel nozzle; and a plurality of swirl vanes disposed in the second annular passage between the outer shroud and the central hub, wherein an interior of each swirl vane of the plurality of swirl vanes is configured to route a first air flow into the first annular passage, an exterior of each swirl vane of the plurality of swirl vanes is configured to swirl a second air flow along the second annular passage, and the flow conditioner in the first annular passage is disposed between the plurality of swirl vanes and an outlet of the fuel nozzle.
 18. The system of claim 17, comprising a gas turbine engine, wherein the gas turbine engine comprises the fuel nozzle, a combustor having the fuel nozzle, a compressor, and a turbine.
 19. The system of claim 17, wherein the flow conditioner comprises a plurality of the straightening vanes each having a turn gradually directed along the longitudinal axis in a downstream direction toward the outlet of the fuel nozzle, wherein the flow conditioner comprises the perforated sheet or mesh screen, or the multi-passage body having the plurality of passages generally parallel with the longitudinal axis.
 20. The system of claim 17, comprising a plurality of premixing tubes disposed downstream from the flow conditioner, wherein each tube of the plurality of premixing tubes comprises an air inlet, a fuel inlet, and an air-fuel mixture outlet. 